In telecommunication networks, telecommunication subscribers are provided with a large number of services. Such services regularly involve data transfers taking place between a service provider (for example a service server) and a service user (for example a communication terminal belonging to a telecommunication subscriber). Such data transfers can be used to transfer, by way of example, film data, audio data, message data, market-price data or similar financial information from a service-providing service computer to the service-using communication terminal. In modern communication networks (which are designed on the basis of GPRS or UMTS specifications, for example), the data are transferred in the form of data packets between the service computer and the communication terminal (packet switched data transfer). Mobile communication terminals (e.g. mobile telephones, personal digital assistants or portable computers with a mobile radio interface) can naturally be operated at various locations and hence in various mobile radio networks while using services.